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Document lease abandonment and reallocation.

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Ted Lemon 2000-12-28 23:29:47 +00:00
parent 4f76762762
commit a25a18d772
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server/dhcpd.conf.5
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@ -344,6 +344,33 @@ immediately allocated to the client. If the address is available for
allocation but has been previously assigned to a different client, the
server will keep looking in hopes of finding an address that has never
before been assigned to a client.
.PP
The DHCP server checks IP addresses to see if they are in use before
allocating them to clients. It does this by sending an ICMP Echo
request message to the IP address being allocated. If no ICMP Echo
reply is received within a second, the address is assumed to be free.
This is only done for leases that have been specified in range
statements, and only when the lease is thought by the DHCP server to
be free - i.e., the DHCP server or its failover peer has not listed
the lease as in use.
.PP
If a response is received to an ICMP Echo request, the DHCP server
assumes that there is a configuration error - the IP address is in use
by some host on the network that is not a DHCP client. It marks the
address as abandoned, and will not assign it to clients.
.PP
If a DHCP client tries to get an IP address, but none are available,
but there are abandoned IP addresses, then the DHCP server will
attempt to reclaim an abandoned IP address. It marks one IP address
as free, and then does the same ICMP Echo request check described
previously. If there is no answer to the ICMP Echo request, the
address is assigned to the client.
.PP
The DHCP server does not cycle through abandoned IP addresses if the
first IP address it tries to reclaim is free. Rather, when the next
DHCPDISCOVER comes in from the client, it will attempt a new
allocation using the same method described here, and will typically
try a new IP address.
.SH DHCP FAILOVER
This version of the ISC DHCP server supports the DHCP failover
protocol as documented in draft-ietf-dhc-failover-07.txt. This is